Cathode-ray circuit



June 7, 1949. w, HALL 2,472,209

CATHODE-RAY CIRCUIT Filed Sept. 6. 1944 JAIN-ill I8 I INVENTOR. WILLIAM M. HALL ATTORNEY Patented June 7, 1949 UNITED STATES PATENT OFFICE 10 Claims.

The present invention relates broadly to cathode ray oscillograph circuits, and more particularly to circuits for increasing the intensity of the signal trace on the screen of a cathode-ray tube in response to impulses of extremely short duration.

The screen of a cathode-ray tube consists of a thin layer of luminescent material which, under bombardment by rapidly moving electrons, gives rise both to fluorescence or emission of light during bombardment and to phosphorescence or emission of light after bombardment. Because of build-up characteristics of the screen material, in conventional cathode ray tube circuits, a short signal pulse applied to the control grid of the tube will not instantaneously build up the screen flash to peak amplitude. Where pulses in the order of one microsecond are employed, such as those utilized for pulse-echo object location applications, the duration of the pulse is less than the finite time required before screen flash is attained. Accordingly, the flash intensity of fluorescence will be proportional both to the signal strength and its time of duration.

It is, therefore, an object of the present invention to provide a cathode-ray tube circuit for increasing the intensity of signal trace upon the application of sharply defined impulses.

Another object of the present invention is to provide a circuit of the above type which does not substantially affect the signal-to-nolse ratio of the screen trace.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, wherein like parts are indicated by like reference numerals. The scope of the invention will be pointed out in the accompanying claims.

In the accompanying drawings:

Figure 1 is a schematic circuit diagram of a preferred embodiment of the present invention,

And Figure 2 is a schematic circuit diagram of another preferred embodiment of the present invention.

Referring now to the drawing and more particularly to Figure 1, an intensity control circuit for a cathode ray tube Ill is provided comprising a diode vacuum tube H, a capacitor l2, and a resistor 13. The signal pulse I4 is applied to terminals l5 and is of a polarity rendering diode ll conductive through coupling capacitor [6 and capacitor l2. The resultant charge on capacitor I2 is impressed upon the grid control circuit of cathode ray tube l9, being maintained thereon for a period determined by the time constant of capacitor l2 and shunt resistor l3. Capacitor I2 is unable to discharge through diode II and must, therefore, discharge through resistor l3.

During the time of the signal pulse and the discharge period of capacitor I2, the signal trace will remain intensified; the leading edge of the signal trace will appear steep while the trailing edge will assume the shape of an exponential decay. By adjusting the time constant of capacitor l2 and resistor l3, the holding voltage may be maintained until screen fluorescence has been reached. In practice, it has been found that this holding period should be from 10 to microseconds duration, in which case capacitor l2 may be small in the order of five micro-micro-farads, and resister l3 may be large in the order of five megohms.

Another method of increasing the intensity of the screen trace and one which will improve the shape of the trailing edge of the signal present in Figure 1 is disclosed in Figure 2. It will be seen that resistance l3 of Figure 1 has now been supplanted by a triode H which functions essentially as a clamping tube. The grid of triode I! is initially biased beyond cutoff by a voltage obtained from a battery l8. A pulse delay line I9 is provided, one end of which is connected to the plate of diode H, the other end thereof being connected to the grid of triode I! through a couplng capacitor 20. The delay line I9 is terminated in its characteristic impedance by a resistor 2|. When an impulse is applied to terminals l5, condenser I2 is charged through diode ll thereby impressing an intensifying voltage on the grid of cathode ray tube l0. When the incoming pulse passes delay line l9 after an interval determined by the length thereof, it applies a voltage to the grid of triode I! having a magnitude and polarity which overcomes the bias of battery l8 thereby rendering said triode conductive, whereupon condenser l2 proceeds to discharge therethrough. Inasmuch as delay line i9 is terminated in its characteristic impedance, no reflection of the incoming pulse is possible; hence interference with succeeding incoming signals is averted. It will be noted that no steady plate potential is applied to the space-current path of triode ll, the sole exciting potential thereon being the charge on capacitor l2.

It is evident that increasing the length of the delay line H) will cause an increase of screen intensification. The advantage of incorporating the clamping tube I! into the circuit is to cut off the trailing edge of the tube trace, thus improving the signal-to-noise ratio.

While there has been described what are at present considered preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims, to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. Apparatus for increasing the intensity of signal trace on a cathode ray tube screen comprising a capacitor connected in the control grid circuit of the cathode ray tube, a triode'vacuum tube having its plate circuit connected across said capacitor, a diode vacuum tube, an artificial 1 transmission line, and means for simultaneously applying an incoming pulse to said condense"? through said diode and to the grid of said triode tube through said transmission line" whereby a' voltage is maintained on the control grid of said cathode ray tube for a period determined by the length of said line.

2. A network for increasing the duration of space'd discrete"signals, comprising a pair of in put terininals to which said signals are applied,

a capacitor connected to said terminals in series with unidirectional conducting means whereby saidcapaoitor is charged by said signals, a normall'ynonfc'onducting electron tube having its space-ourr'enfpath' connected across said capacitor ,-a circuit connected to said input ter-*' minals' for' rendering said tube conducting in re-' sponsdto said-signals, said circuit having delay meairis"therein whereby the charge on said capacitoris retained for a period determined by the delay time of said delay means, and an output circuit fdrs'aid network connected across said ca-' pacitor.

3.;A;f1etwork"for increasing the duration of spacedpulses comprising "a pair of input terminals to 'Whi'chsaid' pi'ilsesare'applied, a capacitor connectd't'o said terrninals in series with unidirectional c'onductin'g"means whereby said signals chargesaid capacitorjan electron tube including at 'la'st 'one control grid and having its spacecurrent path connected across said capacitor, a cutofi p ote'fitial on said'grid for normally blocking'sa'id spa'ce current path, and a circuit responsive'to said pulses for unblocking said space I current p'ath,' 'said=circuit' including a delay line connected between said input terminals and said control'grid'; whereby the charge on said capacitor is maintained for a period determined by the delay producedby said delay-line, and an output circuit for-said"networkconnected across said capacitor. 4. A network for increasing the duration of spaced puls'es comprising a pair of input terminals to which sai-dpulses 'are applied, a capacitor connectedto said terminals'in series with unidirectional con'ductingmeans for applying said signals to charge said capacitor, an electron tube including'at least one control grid and having its space=current path "connected across said capacitor and excited solely by the charge on said capacitorj-a cutoff potential on said grid for normall 'blocking said space-current path, and a circuit-responsive to said pulses for unblocking said space-current path, saidcircuit comprising a delay-line connected between said input terminals and said control'grid, whereby the charge on said capacitor is maintained for a period determined by the delay produced by said delay line, andan output circuit for said network connected across said capacitor.

5. A pulse widening circuit comprising a con denser-Which'maybe charged by an incoming pulse; a delay network connected to said condenser to be operative after a predetermined interval,;and-a radio tube connected to said delay network through which said condenser is dis-- charged after said interval.

6. A pulse widening circuit comprising a condenser charged by an incoming pulse, a delay network connected across said condenser, a radio tube having an anode, grid andcathodewith its anode-cathode circuit connected across said condenser and its grid connected to said delay network, whereby a potential is impressed upon said grid to discharge said condenser through said andde catlidde circuit after a predetermined intervalw- 7. A network'for spaced discrete pulses comprising a-pair of circuits adapted to be excited in parallel from said source, an asymmetrically conducting"ele'ment in only one of said circuits, a capacitor connected in series with said element, said elerii'ent being bonnected "to permit rapid charging of said capacitor by said pulses, a nor 'f "witch for discharging said capacitor,

mall-yop'e' 0 and'meansin' the' othe'r'o'f said circuits and re-* sponsive tosaid-"pulses= to provide "discrete potentials which are delayed relative to said pulses,

pacitor'.

8. A network rorspaced discrete' pulses 'c'om prising-Pd paw-"of circuits adapted'to be excited in parallel fron1=""said* s'ource',an asymmetrically" conducting element-in only one of said circuits, a

capailtoncon'necte'd in'series with"said'element,

said"element*being* connected'to permit charging of saidcap'acitor' by said pulses, a space-discharge path 'of 'noriiially high-impedance connected across saidwapa'citoryand 'me'ansfin the otherof' said'circuits-and-responsive to said pulses to pro-' vide 'discrete' poteritials whichare delayed rela'-' tive to said' pulses; 'and mearisflresponsive to each of 'said' p'otentials'to' l'ower'the "impedance of said paraller:from'saidsourcela conducting diodein only one of said'circuits, a" capacitor connected in series with said diode; said" diode being poled to permit=charging of saidc'apacitfl by said pulses; a

normally non-conducting s'pace 'dis'char'ge' path" for discharging said capacitor, and means in the other of 'said circuits and responsive to said pulses to *prcivide *discrete potentials which are delayd'relaltive'to 'saidpulses; and means responsive to each-of 'sai'd"potentials"to render said space=discharge pathconducting thereby' to 'discharge said capacitor.

10. A network as set forth in claim 9, whereinsaid space-discharge-pathcomprises an electron tube having anodeand cathode electrodes respectively connected to opposite sides of said capacitor, there being no-anode biasing potential connected between said cathode and anode.-

WILLIAM M. HALL.

REFERENCES l CITED The'followingreferences' are of record in the file 'of this patent'z 

